The long-term objectives of the proposed studies are to elucidate molecular mechanisms that underlie the complex biology of opiate drug action and to develop expertise in modern molecular and cell biological methods. These studies are directly relevant to the biology of drug addiction. In addition, these studies are of general relevance to the biology of G protein-coupled receptors, which represent the largest family of neurotransmitter receptors and are important targets for many classes of drugs. The Specific Aims of the proposed studies are to utilize an established model cell system to 1) Determine the role of dynamin-dependent endocytosis in mediating functional desensitization and resensitization of the mu opioid receptor; 2) Determine the role of dynamin-dependent endocytosis in mediating down-regulation of the mu opioid receptor; and 3) Examine the effect of dynamin-dependent endocytosis on upregulation of cAMP-mediated signal transduction induced by opiate drugs. The methodology includes molecular biological techniques, cell culture and transfection, immunochemical assays of receptor internalization, and biochemical assays of receptor-mediated signal transduction.